Addressing a more sustainable management of water resources involves new policies that
require improved knowledge on water allocations and benefits from the economic and
environmental uses of water. However, environmental uses have been mostly disregarded
in traditional water management, and just recently the maintenance of environmental
water flows is being considered as a key issue in water policies. The aim of this study is
to analyze the spatial and sectoral allocation of water resources in the Ebro Basin (Spain),
in order to inform the debate on the environmental flow in the Ebro mouth. The study
analyzes in detail the irrigation districts using most of the water resources, and the
environmental flow proposals for the river mouth. A hydro-economic model is developed
to analyze the effects of different water allocation mechanisms under combinations of
water availability and environmental flow scenarios. This is an important tool to explore
the tradeoffs and political economy aspects from water reallocation. Results show that
the petition of raising the environmental flow at the Ebro mouth during droughts by the
downstream state (Cataluña) would be very costly for all irrigation districts in the basin.
One alternative for the downstream state to gain the support of the rest of states for raising
the environmental flow would be to compensate the losses of irrigation districts in
upstream states.